Power assisted steering gear

Abstract

A power assisted steering gear has a toothed part 1 such as a pinion coupled through a torque responsive rod 12 to an input shaft 4 so that rotation of the shaft 4 rotates the pinion 1 to drive an output member having a servo motor associated therewith. Fluid flow to the servo motor for power assistance is controlled by the valve 6 by displacement of component parts of the valve during relative rotation between the input shaft 4 and the pinion 1 as permitted by the rod 12. The valve 6 and pinion 1 form a unified assembly 7 carried on the shaft 4 and which is inserted into and removed from the housing 3 (by way of a side port 15) in unit manner. The assembly 7 is retained in the housing 3 solely by means, such as a spring clip 25, which is readily accessible from the exterior of the housing. The unified assembly 7 is rotatably borne in the housing by bearings 16 and 17 which may form part of the assembly for removal therewith or be retained within the housing following removal of the unified assembly. The bearing 16 journals a shaft part 19 formed by an extension of the rod 12 through the pinion 1.

We claim: 
     
       1. A power assisted steering gear comprising a housing defining a chamber and having an opening therein at one side thereof, an input shaft extending into said chamber through said opening, a toothed part rotatably mounted in said chamber for driving an output member in response to rotation of said input shaft, said input shaft and said toothed part being capable of restricted rotation relative to each other, valve means located in said chamber and responsive to relative rotation of said input shaft and toothed part for controlling fluid flow to a servo motor associated with said output member to provide power assistance to movement thereof, means attaching said valve means and said toothed part and said input shaft to form in a single unitary assembly for insertion into said chamber through said opening as a unitary assembly and for removal from said chamber through said opening as a unitary assembly, a single retaining means for retaining said unitary assembly in said chamber and preventing removal thereof from said chamber through said opening, said single retaining means being located at said one side and comprising a releasable means releasable to allow for removal of said unitary assembly through said opening. 
     
     
       2. A gear as claimed in claim 1 in which the toothed part and valve means are disposed axially in tandem so that during insertion of the unitary assembly into the chamber the toothed part leads the valve means. 
     
     
       3. A gear as claimed in claim 1 in which the chamber comprises a stepped axially extending bore the larger diameter bore part of which is located adjacent to the one side, one of the toothed part and valve means being located in the larger diameter bore part and the other being located in the smaller diameter bore part. 
     
     
       4. A gear as claimed in claim 3 in which the toothed part and valve means are disposed axially in tandem and the toothed part is located in the smaller diameter bore part. 
     
     
       5. A gear as claimed in claim 3 and comprising a fluid seal between the unitary assembly and the housing, said seal being seated in an annular shoulder formed between said stepped diameter bore parts. 
     
     
       6. A gear as claimed in claim 1 further comprising first and second axially spaced bearing means, said first and second bearing means rotatably mounting the toothed part and the valve means in the housing.   
     
     
       7. A gear as claimed in claim 6 in which at least one of said first and second bearing means is mounted in the housing to rotatably accommodate the unitary assembly during insertion of the assembly into the chamber and that said at least one bearing means is retained in the chamber following withdrawal of the unitary assembly therefrom. 
     
     
       8. A gear as claimed in claim 7 in which the toothed part and valve means are disposed axially in tandem so that during insertion of the unitary assembly through the one side the toothed part leads the valve means and wherein the first bearing means is mounted in the chamber to rotatably support the toothed part as the unitary assembly is inserted into the chamber. 
     
     
       9. A gear as claimed in claim 8 in which the toothed part comprises a bearing shaft extending from the side thereof axially remote from the valve means and which bearing shaft is journalled in the first bearing means. 
     
     
       10. A gear as claimed in claim 6 in which the second bearing means is part of the unitary assembly. 
     
     
       11. A gear as claimed in claim 10 wherein said second bearing means is received between an annular shoulder provided on the housing and said retaining means to thereby prevent axial displacement of the unitary assembly in the housing. 
     
     
       12. A gear as claimed in claim 1 in which the retaining means comprises a closure cap or plate removably retained on the housing and having an aperture through which the input shaft extends. 
     
     
       13. A gear as claimed in claim 12 in which the retaining means comprises a closure cap screw threadedly engaged with the housing. 
     
     
       14. A gear as claimed in claim 12 in which the retaining means comprises a closure plate and a spring clip which engages with the housing to retain said plate. 
     
     
       15. A gear as claimed in claim 1 in which the input shaft and toothed part of the unitary assembly are capable of restricted rotation about the shaft axis relative to each other and are rotationally biased relative to each other to oppose said restricted rotation and to a neutral condition of the valve means and wherein the valve means comprises first and second valve parts which are displaceable with respect to each other and in response to said rotational displacement between the input shaft and the toothed part to control fluid flow through the valve means. 
     
     
       16. A gear as claimed in claim 15 in which the first and second valve parts are rotationally displaceable, one in unison with the toothed part and the other in unison with the input shaft. 
     
     
       17. A gear as claimed in claim 16 in which the first and second valve parts comprise a valve core and a valve sleeve within which the core is rotatably received. 
     
     
       18. A gear as claimed in claim 17 in which the valve sleeve is integral with the toothed part. 
     
     
       19. A gear as claimed in claim 15 in which the means attaching the valve means, the toothed part and the input shaft comprises a resilient axially extending torque responsive rod coupled at one end region for rotation with the input shaft and at the other end region for rotation with the toothed part, said rod providing for rotational biasing between the input shaft and the toothed part. 
     
     
       20. A gear as claimed in claim 19 comprising first and second axially spaced bearing means, said first and second bearing means rotatably mounting the toothed part and the valve means in the housing, said toothed part and valve means being disposed axially in tandem so that during insertion of the unitary assembly through the one side the toothed part leads the valve means, said toothed part being tubular and the torque responsive rod extending coaxially therethrough, an end of said rod projecting axially from the toothed part on the side thereof axially remote from the valve means, said end providing a journal by which the toothed part end of the unitary assembly is rotatably borne by the first bearing means. 
     
     
       21. A gear as claimed in claim 1 in which the toothed part comprises a pinion. 
     
     
       22. A gear as claimed in claim 1 wherein said releasable means is removably received in said housing.